Alicia Álvarez

Muscular Anatomy of the Forelimbs of the Lesser Grison (Galictis cuja), and a Functional and Phylogenetic Overview of Mustelidae and Other Caniformia

The extrinsic and intrinsic forelimb musculature of the lesser grison (Galictis cuja), a short-legged mustelid of southern South America, is studied for the first time. We present descriptions, muscular maps, and weight data. Muscular anatomy description of the lesser grison provides the framework for discussing the myological diversity of mustelids and other caniforms, for addressing nomenclatural problems (such as synonymy and homonymy), and for highlighting some functional and phylogenetically informative traits. We recognize in the lesser grison features shared by all mustelid species, and some other caniforms, especially mephitids, such as the presence of rhomboideus profundus, an angular head of triceps brachii, and, apparently, the absence of a flexor digitorum brevis manus. An unexpected record of articularis humeri, a proximal origin of the brachioradialis, and the absence of the tensor fascia antebrachii are recorded for this species. As other ictonychines and mustelines, Galictis cuja possesses stronger and subdivided protractors and sagittal rotators of the forelimbs, as well as shoulder and elbow extensors. These features allow for resistance in landing during bounds and increase the stride length during epigean and subterranean crouched locomotion. Powerful neck musculature assists during hunting and carrying of prey. Weakness of some retractors and intrinsic flexors is related to a relatively minor importance of the forelimbs as propellers during bounding and the lack of other specializations. The configuration of the rhomboideus and the absence of coracobrachialis seem to be informative at the subfamiliar level within Mustelidae. The comprehensive and comparative review of available information leads us to propose possible solutions to old nomenclatural problems and of identification. This allows us to reassess of some myological features as diagnostic of caniform clades.

Contrasting Phylogenetic and Diversity Patterns in Octodontoid Rodents and a New Definition of the Family Abrocomidae

Octodontoidea is the most species-rich clade among hystricomorph rodents. Based on a combined parsimony analysis of morphological and molecular data of extinct and extant species, we analyze the history of South American octodontoids and propose ages of divergence older than interpreted so far. Early Abrocomidae are recognized for the first time, and a new definition of the family is provided. Traditionally accepted fossil-based times of origin for the southern clades are reinterpreted as later stages of differentiation markedly uncoupled from the origin, differentiation implying specializations for open environments as shown in a morphospace of skull variation. Origin of crown groups is also strongly uncoupled from origin of clades as a consequence of extinction of deep lineages. In the resulting diversity pattern of modern southern clades of octodontoids, the combination of greater disparity, less content of evolutionary history, and lower taxonomic diversity, compared to their northern counterparts, appears at first counterintuitive. We propose that primary components of diversity derived from evolutionary transformation or anagenesis, on the one hand, and from cladogenesis and extinction, on the other, should not be considered associated, or at least not necessarily. Certain patterns of relationships between these distinct components could be driven by environmental dynamics. Like environments, octodontoid diversity would have been more stable in northern South America, whereas in the south, both strong adaptive change and extinction would have been triggered by emerging derived environments.

The Role of Evolutionary Integration in the Morphological Evolution of the Skull of Caviomorph Rodents (Rodentia: Hystricomorpha)

The mammalian cranium is a complex structure composed by three partially independent modules: face, cranial base and cranial vault. At the same time, it interacts with the mandible by sharing the masticatory function. Since these units develop and work together, their function and evolution may occur through correlated changes. Here, we assessed the patterns of evolutionary shape variation and covariation (i.e. integration) of cranial modules and mandible among the highly ecomorphologically diverse caviomorph rodents, and the potential evolutionary consequences on the morphological evolution of this clade. Three-dimensional geometric morphometrics was used to describe cranio-mandibular shape. The phylogenetic signal and evolutionary allometric component of morphometric variables were analyzed; in addition, evolutionary covariation among cranial modules and mandible was assessed using phylogenetic comparative methods. Significant phylogenetic signal and evolutionary allometry were detected. Large covariance values, involving coordinated breadth increase as the main shape change, were recorded between cranial vault and base, followed by cranial vault and face, and face and mandible. Since the basicranium may be the main cranial integrator, the overall widening of the cranial base, derived from the enlargement of the auditory bullae, could be influencing the integrated evolution of skull. In caviomorphs, the cranio-mandibular morphological evolution would be the outcome of a tight covariation among the modular units, and this could be driven by several factors such as allometry and specializations to environmental niches.

The Functional and Phylogenetic Implications of the Myology of the Lumbar Region, Tail, and Hind Limbs of the Lesser Grison (Galictis cuja)

Mustelids are a morphofunctionally diversified group. However, there are no descriptions of the postcranial musculature of South American mustelid species except for some comments from the 19th century. Here, we present the first description of the myology of the hind limbs, and lumbar, sacral, and caudal regions of the lesser grison (Galictis cuja), a short-legged South American mustelid, including muscle maps and weight data. We interpret the function and the evolution of several muscular features within a comparative framework and through the optimization of these traits onto a phylogeny. The configuration of the axial musculature (e.g., m. quadratus lumborum with short bundles, heavy iliocostalis, and forward originated sacrocaudalis dorsalis) and the presence of strong ankle musculature are features shared with mustelines and, to a lesser degree, with other musteloids. These could be related to a high mobility of the axial skeleton and strong control of the movement of the ankle joint, in relation to the acquisition of epigean bounding gaits, a crouched locomotion, and enhanced maneuverability inside burrows. We recorded many phylogenetically significant traits, shared with other arctoids (e.g., subdivision of m. gluteus profundus and semimembranosus, presence of a single belly for m. sartorius, and absence of articularis coxae) or exclusively musteloids (e.g., frequent fusion between m. piriformis and gluteus medius). Some features (e.g., restricted origin of the caudal belly of the m. semitendinosus, absence of gluteofemoralis, and unusually complex fibularis brevis) seem to be derived conditions acquired in some mustelid clades. Our results sustain the value of myological data for functional and phylogenetic studies.

First Approach to the Paleobiology of Extinct Prospaniomys (Rodentia, Hystricognathi, Octodontoidea) Through Head Muscle Reconstruction and the Study of Craniomandibular Shape Variation

Abstract†Prospaniomys is a basal octodontoid recorded in the early Miocene in Patagonia (Argentina; Colhuehuapian SALMA). Nearly complete cranial and mandibular remains known for this genus provide a unique opportunity to explore its paleobiology. For this, masticatory muscles were reconstructed and craniomandibular shape variation assessed. While such reconstruction indicates that most masticatory muscles would have presented moderate development, both the masseter lateralis and posterior muscles were poorly developed. In contrast, we found that the temporalis muscle was well developed, while conspicuous postorbital constriction, postorbital processes, and superior temporal lines revealed a substantial orbital portion of this muscle. According to geometric morphometric results, craniomandibular shape was interpreted as generalized. Features such as shortened palate, narrower bizygomatic width, orthodont incisors, enlarged incisive foramina, and a shallow jaw could be linked to epigean habits. The moderate development of auditory bullae in Prospaniomys suggests that it is unlikely that it may have lived in extreme arid environments. Additionally, based on its generalized dental morphology, an omnivorous or generalized herbivorous diet that may have included leaves, fruit, and potentially animal matter was inferred. By the early Miocene, Patagonia experienced the initial expansion stage of arid-adapted vegetation, with grasses present in low amounts and abundant forests. Generalized habits and soft and non-abrasive diet suggest that Prospaniomys was possibly associated with more closed environments. Morphology alone cannot be used as an environmental proxy, but it could undoubtedly contribute to the interpretations based on data provided by paleobotanical and geological frameworks in studies on the evolution of environments.

Myology of the Head, Neck, and Thoracic Region of the Lesser Grison ( Galictis cuja ) in Comparison with the Red Panda ( Ailurus fulgens ) and Other Carnivorans: Phylogenetic and Functional Implications

The lesser grison (Galictis cuja) and the red panda (Ailurus fulgens) represent two opposed morpho-functional musteloid extremes. The mid-sized lesser grison is primarily terrestrial, a frequent burrow-dweller, and carnivorous, while the larger, scansorial red panda eats bamboo. This study documents the axial myology of these species, including muscle descriptions, weights, and optimizations. Muscle maps are also provided for the lesser grison, representing the first axial maps for a wild-caught carnivoran. The functional analyses revealed that G. cuja, contrary to A. fulgens, possesses longer, stronger, and subdivided neck muscles. It also possesses a thoraco-lumbar iliocostalis system that is more developed than the longissimus complex, and numerous, robust, and laterally inserted deep bellies of the cervical and thoracic transversospinalis systems. These specializations allow powerful neck movement during hunting and transport of heavy prey as well as axial flexibility, facilitating bounding gaits and lateral movements while navigating subterranean galleries. Some myological traits of the red panda differ from those expected in a highly herbivorous taxon (e.g., m. sternocephalicus, m. masseter), and may reflect its depredatory ancestry. The optimization analysis revealed phylogenetically informative traits across Carnivora, including the absence of m. longissimus capitis in Mephitidae, the absence of spinous thoracic origins for m. biventer cervicis in Musteloidea, and the presence of a relatively lateral insertion of m. rectus dorsalis capitis intermedius in the clade Ictonychinae+Lutrinae+Mustelinae. This study reveals key associations between axial myological and osteological features that will prove useful for future studies of carnivorans.

Reading shell shape: implications for palaeoenvironmental reconstructions. A case study for bivalves from the marine Quaternary of Argentina (south-western Atlantic)

Most research on bivalves from the south-western Atlantic used morphological (shell) characters for taxonomic discriminations. Dominant Veneroids from Argentinian Quaternary coastal deposits exhibit wide morphological variation – often making objective discriminations difficult/impossible, which could be objectively described and compared through geometric morphometrics techniques. This work focuses on comparison of geometric morphometrics methods applied to fossil and modern shells, to assess inter- and intra-generic variations. Three approaches were considered: landmarks (L), semi-landmarks (SL) and outlines. Shell shape analyses for different time spans (Pleistocene, fossil Holocene and modern) and areas (Patagonia and Bonaerensian) showed that Elliptic Fourier analysis (EFA), Landmarks and Landmarks plus Semilandmarks (L+SL) can discriminate at generic levels: Mactra, Mulinia (Mactridae) vs. Pitar, Protothaca, Eurhomalea, Clausinella (Veneridae). L and L+SL are powerful for inter/intraspecific distinctions of Mactra. Variability of Mactra isabelleana includes the remaining nominal ‘species’ (transitional morphs). Causal environmental factors of (phenotype) variation could be addressed for modern environments (substrate, salinity and energy). Subtrigonal-inflated shells predominate in muddy, quieter, shallow mixo-polyhaline waters; ovate-elongate-compressed in sandy, poly-euhaline, deeper habitats. Differential spatial distribution (and abundance) across time responds to Late Quaternary high sea-level stands: transgressive maxima allowed higher salinity in marginal-marine areas and optimal conditions for Mactra isabelleana contrasting with scarcer records in the Mar Argentino today.

A novel series of forepaw muscles for mammals observed in the Patagonian weasel Lyncodon patagonicus

The intrinsic autopodial musculature of mammals is composed of a relatively stable number of muscular groups. Here, we present the first myological studies of Lyncodon patagonicus, a South American mustelid that is morphologically and ecologically poorly known. The typical intrinsic muscles of the manus of Lyncodon are similar to those of its sister taxon Galictis, although there exist few variations, including additional subdivisions and relatively more distal insertions in some muscles. A striking feature is the presence of a novel series of forepaw muscles never before described for mammals. These muscles, named here mm. flexores digitorum proprii manus, are represented by a medial and a lateral belly for each digit and are located immediately distal to the mm. flexores breves profundi. They are located distally alongside the tendons of the latter, along the palmar aspect of the phalangeal series, and they insert onto the flexor tubercle of the distal phalanx of each digit. We propose that the incorporation of these muscles in the forepaw musculature of Lyncodon, in addition to some other osteo-myological features, imply a distinctive morpho-functional adaptation to increase the force of flexion and independence of digital movements likely used to grasp prey during hunting. This hypothesis should be confirmed by future ecological and behavioral studies on this species.

Shape variation in presacral vertebrae of saltasaurine titanosaurs (Dinosauria, Sauropoda)

Titanosaurs were small- to giant-sized sauropods, highly derived and highly pneumatic. Using morphometric analyses, we studied differences in shape of the presacral vertebral centra in some of these sauropods, especially in saltasaurines, and compared asymmetry patterns in lateral pneumatic foramina (LPF) between these titanosaurs and avian and non-avian theropods. Geometric morphometric analyses showed that the cervical centra tend to be elongated and dorsoventrally short, with an elliptical LPF located in the middle of the centrum; dorsal centra tend to be short and higher than the cervical centra, with the LPF slightly displaced to the anterior region. Shape variation can be described as a result of the ordering of the vertebrae within both the cervical and dorsal sequences, and therefore these methods can be applied to predict the position of isolated vertebrae. A persistent pattern of asymmetry among LPF was observed when length–height indexes were plotted. The right LPF are usually larger than those on the left side in the cervical vertebrae (except in Saltasaurus loricatus) but variable in the dorsal vertebrae. We propose an explanation of this asymmetry based on the asymmetric arrangement of viscera and late development of the respiratory (and air sacs) system.

Why pacaranas never say no: analysis of the unique occipitocervical configuration of †Tetrastylus intermedius Rovereto, 1914, and other dinomyids (Caviomorpha; Dinomyidae)

ABSTRACT Dinomyidae is a South American caviomorph family that was a very diverse group starting in the Miocene, but is now represented by a single species, Dinomys branickii Peters, 1873. An exclusive feature of dinomyids, not recorded in other mammals, is the presence of accessory articular structures lateral to the occipital condyles, termed paracondyles. In a 1916 study of †Tetrastylus intermedius Rovereto, 1914, an extinct dinomyid from northwestern Argentina, Carlos Ameghino suggested that the paracondyles enhance the support of a large and heavy head. At present, this is the only proposal to explain the presence of these structures. In order to validate this hypothesis, we performed descriptive, metric osteological analyses, and muscular reconstructions of the occipital and cervical regions of †T. intermedius, D. branickii, and other dinomyids, in a comparative context of rodent diversity. We confirmed that, similar to some other living rodents, D. branickii possesses a relatively large head. Conversely, †T. intermedius possesses a size-proportionate head and has larger paracondyles than D. branickii. Our analyses suggested that fossil dinomyids would have performed more marked sagittal movements than D. branickii, and that paracondyles and the whole occipitocervical configuration of dinomyids are specialized for restriction of movements of the head and neck. We rejected the single previous hypothesis and proposed an alternative and novel one, in which paracondyles, and other occipitocervical traits present in dinomyids, as well as in erethizontids, could be related to restricted movements and linked to ecological convergences for stealthy and slow arboreal locomotion.